test: improve internal/buffer.js test coverage

Added tests buffer.js methods to write 48 bit value to
improve test coverage.

PR-URL: #21061
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Lance Ball <lball@redhat.com>

test/parallel/test-buffer-readint.js

@@ -169,7 +169,7 @@ const assert = require('assert');
   });
 
   // Test 1 to 6 bytes.
-  for (let i = 1; i < 6; i++) {
+  for (let i = 1; i <= 6; i++) {
     ['readIntBE', 'readIntLE'].forEach((fn) => {
       ['', '0', null, {}, [], () => {}, true, false].forEach((o) => {
         assert.throws(

test/parallel/test-buffer-readuint.js

@@ -130,7 +130,7 @@ const assert = require('assert');
   });
 
   // Test 1 to 6 bytes.
-  for (let i = 1; i < 6; i++) {
+  for (let i = 1; i <= 6; i++) {
     ['readUIntBE', 'readUIntLE'].forEach((fn) => {
       ['', '0', null, {}, [], () => {}, true, false].forEach((o) => {
         assert.throws(

test/parallel/test-buffer-writeint.js

@@ -162,6 +162,21 @@ const errorOutOfBounds = common.expectsError({
   });
 }
 
+// Test 48 bit
+{
+  const value = 0x1234567890ab;
+  const buffer = Buffer.allocUnsafe(6);
+  buffer.writeIntBE(value, 0, 6);
+  assert.ok(buffer.equals(new Uint8Array([
+    0x12, 0x34, 0x56, 0x78, 0x90, 0xab
+  ])));
+
+  buffer.writeIntLE(value, 0, 6);
+  assert.ok(buffer.equals(new Uint8Array([
+    0xab, 0x90, 0x78, 0x56, 0x34, 0x12
+  ])));
+}
+
 // Test Int
 {
   const data = Buffer.alloc(8);

test/parallel/test-buffer-writeuint.js

@@ -110,6 +110,17 @@ const assert = require('assert');
   assert.ok(data.equals(new Uint8Array([0x6d, 0x6d, 0x6d, 0x0a, 0xf9, 0xe7])));
 }
 
+// Test 48 bit
+{
+  const value = 0x1234567890ab;
+  const data = Buffer.allocUnsafe(6);
+  data.writeUIntBE(value, 0, 6);
+  assert.ok(data.equals(new Uint8Array([0x12, 0x34, 0x56, 0x78, 0x90, 0xab])));
+
+  data.writeUIntLE(value, 0, 6);
+  assert.ok(data.equals(new Uint8Array([0xab, 0x90, 0x78, 0x56, 0x34, 0x12])));
+}
+
 // Test UInt
 {
   const data = Buffer.alloc(8);